流体油画

Model the brush as N bristles, each a chain of about ten vertices stored in textures, and solve distance, bending and canvas-plane constraints with position-based dynamics in fragment shaders as the brush follows the pointer. Where bristles touch the canvas, splat velocity and paint into a paint texture. Run a standard grid fluid step on the paint (advect, compute divergence, Jacobi pressure iterations, subtract gradient) restricted to the region near the brush for speed. Store colour in RYB and convert with a trilinear lookup for subtractive-looking mixes, then derive normals from paint thickness and shade with a simple microfacet light.